Demonstrators clashed with police on the streets of Athens and Madrid on Wednesday in an upsurge of popular anger at new austerity measures being imposed on two of the euro zone's most vulnerable economies. In some of the most violent confrontations, Greek police fired tear gas at hooded rioters hurling petrol bombs as thousands joined the country's biggest protest in more than a year. The unrest erupted after nearly 70,000 people marched to the Greek parliament chanting "EU, IMF Out!" on the day of a general strike against further cuts demanded by foreign lenders.